Edited by tkaiser at Thu Jan 15, 2015 07:11 |
bpiuser replied at Thu Jan 15, 2015 05:36
At least I learned also while doing this test ... which is also one of the purposes of the the Banana Pi project
Ok, then the most important lesson to learn is: Don't do this. It's slow, unreliable and costly (compared to an also crappy PC based RAID implementation that features enough native SATA ports eg. outlined in this thread). If you add the costs for the Port Multiplier, PSU and enclosure you will simply realize that you get a more reliable implementation being many times faster and being less expensive using a cheap PC based Mini-ITX solution that features at least a few SATA ports providing superiour speed.
And RAID in such an environment makes no sense at all. It's only about availability ("business continuity") and realiability. Which is not possible with unreliable hardware. You would have to repeat resync/recover tests at least hundred times to know whether your setup with the cheap PM will succeed each and every time an array has to be rebuilt. While this might not be true for another user buying a different (clone of) JMB321 on aliexpress, trusting in your published experiences, believing he has done something regarding data safety (many inexperienced users do so!) and losing the whole array the first time a disk (or the PM... or the single SATA port) fails.
That's the problem with home/SOHO RAID: You trust a setup you can't trust in unless you've proven the realibility many many times. I've seen so many RAID setups failing the last two decades that I want to prevent people from trusting in those unreliable setups. Especially when the whole approach is totally useless. Why RAID-1 when you don't need availability (if you need availability I would consider using a server platform and not a tablet grade hardware like a SBC)? Other RAID levels would make some sense if you want to concatenate the capacity of different disks. But while RAID-5 isn't sufficient for TB HDDs since years, RAID-6 would mean really crappy performance with HDDs behind a cheap PM and RAID-6 in mdraid was broken for almost 5 years without anyone noticing it: https://lkml.org/lkml/2014/8/18/17 (and RAID-6 in btrfs is still not ready for deployment)
Conclusion: If you want it slow, error/failure prone and you like bit rotting as well as frequent data losses... then play with RAID, Port Multipliers, 'servers' without ECC RAM, and so on. Otherwise accept that the minimum requirements for home/SOHO RAID are ECC RAM and the necessary count of SATA connectors as well as a storage implementation that features end-to-end data integrity and can deal way better with disk failures than the brain dead 'resync every unused block' approach mdraid on Linux provides. Then it's time to have a look at HP's N54L (or better) and go with ZFS unless btrfs is ready...